1. Field of the Invention
It known to manufacture ethers by reacting an olefin with methanol in the presence of an acid catalyst. Thus, methyl tertiary butyl ether (MTBE) and methyl tertiary amyl ether (TAME) may be prepared by reacting isobutene and isopentene respectively with methanol in the presence of an acidic cation exchange resin catalyst. This reaction leads to the formation of a reaction product mixture comprising the desired ether together with unreacted methanol, unreacted hydrocarbons and some tertiary alcohol by-product.
It is conventional to add water to this reaction product to effect a phase separation, namely a separation of the ether in an organic hydrocarbon phase and a separation of the alcohols in an aqueous phase. These two phases are generally treated separately in distillation columns in order to effect the separation and recovery of the ether product and to effect the separation of the methanol for recycle to the feed stream which is necessary in order to provide an efficient process.
The tertiary alcohol by-product produced in the reaction is extracted with the methanol into the aqueous phase in the phase separation step. When this aqueous phase is distilled to effect the separation of the methanol for recycle, a tertiary alcohol-water azeotrope is distilled with the methanol and recycled with the methanol to the reactor. This leads to a build-up of water in the feed stream to the reactor with certain deleterious effects on the overall efficiency of the process. In particular, the presence of water in the isoolefin-methanol feed stream to the reactor causes a shift in the course of the reaction leading to the formation of excessive amounts of tertiary alcohol and a suppression or reduction in the yield of the desired ether product from the reaction.
An object of this invention is to provide an improved process for the production and separation of methyltertiary alkyl ethers.
Another object of this invention is to provide a more efficient process including the high conversion of the reactants and utilization of by-products from the reaction.
Another object of this invention is to provide valuable blending agents for motor fuel compositions.
2. Description of the Prior Art
DE-OS No. 2,547,380 discloses a process for the preparation of ethers and the separation of the ether-containing reaction mixture by means of a washing step immediately downstream from the reactor. The sequence of processing steps disclosed in the washing prior to separation by distillation has the advantage that there is no limitation with respect to the amount of methanol present and the complete removal of the alcohol is effected in a single process step without resort to a series of azeotropic distillations.
DE-AS 2,706,465 discloses a two-step process for methyl tertiary butyl ether production.